Field of Invention
This invention belongs to the technical field of nanofabrication, in particular, it relates to a method of preparing nanostructured single crystal silver.
Description of Related Arts
Silver nano-materials, particularly single crystals, are becoming current research hotspots for their excellent electrical conductivities, heat transfer performances as well as the unique catalytic and antibacterial properties. Nano-silver materials will have a promising prospect of application in the fields of electronic components, optical fibers, conductive silver pastes, chemical/biological sensors, chemical catalysis, conductive fillers and the like.
Currently, methods of preparing silver nano-materials mainly include ball grinding method, template method, liquid phase reduction method, electrochemical reduction method and so on. The ball grinding method is capable of preparing flaked silver powder, but lots of additives have to be added during ball grinding, and such ball grinding media impurities cannot be completely removed finally and thus the service performance of said flaked silver powder in electronic pastes would be influenced. The template preparation method can provide a high percentage of silver nano-materials, but its application is somewhat limited since the templating agents have to be removed during the preparation and thus the complexity of the process is increased and the yield of the product is lowered. The liquid phase reaction method suffers from the drawbacks such as a high reaction temperature, environmental pollution, complex preparation process, relatively low product purity and sometimes low crystallinity. So this method is not suitable for extension and application.
After retrieval in the prior art documents, it is found that silver nano-particles and silver single crystals are prepared by reduction in situ within the linear chitosan films, see Acta Phys. Chim. Sin., 2003, 19(5):464-468. In this document, spherical silver nano-particles as well as silver single crystals having triangular or hexagonal appearances are prepared within the linear chitosan films by utilizing photoreduction method and electrochemical method, but the silver single crystals are generated with only one morphology and the yield is low. In the existing work of the inventors, a patent of invention CN102418118A has disclosed a method of electrochemical assisted preparation of nano silver powder in special form, the method comprises immersing a working electrode and a counter electrode, which are used as a cathode and an anode respectively, into a silver ion containing solution or collosol to prepare nano silver powder having various morphologies through electrochemical reaction. However, the prepared nano silver are not single crystals and the silver ions are directly reduced into elemental silver without introducing in new seed crystals during reaction.
The existing difficulties are how to stably prepare nanostructured silver single crystals in bulk at low cost and how to solve the silver surface contamination problem resulted from the use of organic additives such as reductants, templating agents and dispersing agents during preparation. The application value of the silver would be improved greatly if the nano silver materials are prepared with controllable nanostructures morphology. It is therefore still desirable to develop a method which is capable of providing nano silver materials with controllable crystallinity and morphology in high yield.